Researchers find white matter defect link
to dyslexia

Researchers at Stanford University have for
the first time found clear evidence that some
reading problems are tied to a specific defect in
neuron function, according to a report to be
published in the February issue of the journal Neuron.

"We found that adults with reading
deficits have an abnormality in white matter of
the brain, which is vital for transmitting
information between the brain areas involved in
language comprehension," said Psychology
Professor John Gabrieli, who was the senior
researcher on the study team.

The white matter abnormality may indicate that
the neuron's myelin is defective, he said. A
neuron sends vital messages in the brain by
transmitting electrical signals along an extended
appendage called an axon. The axon often is
covered with an insulating fatty sheath, known as
myelin, that speeds up the transmission of the
signals. Myelin is a major constituent of white
matter.

In the study, the researchers examined the
brains of six adults with a history of dyslexia
and 11 adults who had no history of reading
difficulties using a new technique involving
magnetic resonance imaging. The scanner gauged
the cellular structure of the white matter by
measuring the microscopic movement of water
molecules in the brain. Abnormal water movement
indicated faulty white matter, Gabrieli said.

The researchers found that the dyslexic group
had poor functioning white matter that may
therefore slow message transmission in the
regions that are thought to connect the language
processing areas of the temporal and frontal
lobes of the brain.

"We also found that the level of reading
performance of the dyslexic group, as well as the
healthy group, related to white matter
function," Gabrieli said. In the dyslexic
group the poorest readers had the poorest
functioning white matter, and in the healthy
group the poorest readers had the poorest
functioning white matter.

The researchers hope that in the future
physicians will be able to use the noninvasive
imaging technique to identify children at risk
for reading impairments so that they can benefit
from early intervention.

The lead author of the Neuron article
is Torkel Klingberg, a former Stanford
postdoctorate researcher in Gabrieli's
neuroscience lab who is now in the Department of
Neuroscience at Karolinska Institute in
Stockholm, Sweden. Other researchers were Maj
Hedehus and Michael E. Moseley of the Stanford
Department of Radiology and Elise Temple, Talya
Salz and Russell A. Poldrack of the neuroscience
program in the Psychology Department. Poldrack is
now at Massachusetts General Hospital and Salz is
at the Scientific Learning Corp. in Berkeley.